Since gthumb isn't in the repositories for whatever reason I'm looking for an alternative.The single one feature that I absolutely need is to be able to run shell commands when pressing some hotkey on the currently selected image.I've tried eog, shotwell and gwenview, but none of those seems to support that (or I just couldn't figure out how to do that with them).

gthumb has a feature that you can assign actions to a set of hotkeys. Those actions are shell commands, but the special feature is that gthumb provides placeholders that can be used as parameter for those shell commands. For example I can bind the "0" key to the command "someprogram -a %F" then someprogram will be started like this: "someprogram -a /home/me/full/path/to/currently/selected/file.ext". It also has a few other placeholders (i.e. the current directory).

I'm mainly using this to keep track of files and running those commands from inside gthumb is the most comfortable way to do it that I have found. Of course I could open any image viewer and run the shell commands manually but that gets quite annoying after some time.